1. Field of the Invention
The present disclosure generally relates to a developing device, a process cartridge, for use in an image forming apparatus including the image bearing member, such as a copy machine, a printer, a facsimile machine and a multi-function machine capable of copying, printing, and faxing, and more specially, to a developing device for improving the conveyance of a developing agent. The present disclosure ALSO relates to an image forming apparatus using the improved developing device.
2. Description of the Related Art
Conventionally, an image forming apparatus using electrophotography (e.g., copying machine, printer, facsimile, and multi-functional apparatus) includes a developing device, which uses a two-component developing agent composed of toners and carriers (and additives, as required), for example. In the art, in order to downsize such an image forming apparatus, two conveying screws have been adopted that convey circularly the developing agent to each other, while one of the screws supplies the developing agent to the developing roller.
One such image forming apparatus was disclosed in Laid-open Japanese Patent Application No. 2000-89550. The developing device includes a developing roller, two conveying screws, and so on. When toners are consumed by image forming operations, fresh toners are supplied to the developing device through a toner replenishing port equipped at the upper position of the developing device, as required. The two conveying screws agitatingly mix such fresh toners, supplied into the developing device, with a developing agent in the developing device and convey circularly. Some of the developing agent is supplied to the developing roller by one of the conveying screws, which is arranged parallel to the developing roller. The developing agent carried-up on the developing roller may be regulated to a given amount by a doctor blade. Toners in such two-component developing agent adhere to a latent image formed on a photoconductive drum when the developing roller comes to a developing area, at which the developing roller and photoconductive drum face each other. The developing device including such two conveying screws may prevent the developing agent from being unequally distributed to one side within the developing device as in a single conveying screw configuration, because the two conveying screws convey the developing agent circularly to each other. Accordingly, the developing device can adopt a toner replenishing port that occupies not an entire area in between the two rollers but rather only a part of an upper space of the developing device in the longitudinal direction. As a result, adopting the two conveying screw method described above can preferably be used to downsize the developing device and the image forming apparatus.